We look at the division of 409339 by 3 
The aim is to understand the frequency of 3 in 409339.

Step 1:
If we divide 4 by 3, we get 1 and a remainder of 1.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we subtract 3 from 4, we get 1.
Fetch the next digit (0) from the dividend, attach it to 1 and continue: 10 / 3

Moving on to step 2:
When dividing 10 by 3, we get 3 with a remainder of 1.
The next digit of our result is 3. 
Result so far: 13.0
The remainder is 1 after subtracting 9 from 10.
Include the next digit (9) from the dividend after 1, then repeat: 19 / 3

Going ahead to step 3:
When dividing 19 by 3, we get 6 with a remainder of 1.
Put 6 as the next digit of the answer. 
Result so far: 136.0
If we subtract 18 from 19, we get 1.
Include the next digit (3) from the dividend after 1, then repeat: 13 / 3

Moving on to step 4:
3 goes into 13 4 times with a remainder of 1.
Put 4 as the next digit of the answer. 
Result so far: 1364.0
Subtracting 12 from 13 leaves us with 1.
Grab the next digit (3) from the dividend, add it to 1, then carry on: 13 / 3

Moving on to step 5:
The number 3 fits into 13 4 times, leaving a remainder of 1.
Put 4 as the next digit of the answer. 
Result so far: 13644.0
If we take 12 away from 13, we end up with 1.
Grab the next digit (9) from the dividend, add it to 1, then carry on: 19 / 3

Let's proceed to step 6:
3 can be fit into 19 6 times, resulting in a remainder of 1.
Put 6 as the next digit of the answer. 
Result so far: 136446.0
Subtract 18 from 19 to get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 7:
10 divided by 3 is 3 with a remainder of 1.
Write down 3 as next digit of the result. 
Result so far: 136446.3
Subtracting 9 from 10 leaves us with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 8:
10 divided by 3 is 3 with a remainder of 1.
Write down 3 as next digit of the result. 
Result so far: 136446.33
If we take 9 away from 10, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

After the division, we end up with 136446.33 and a remainder of 0.001.